Leukotrienes (LTs) are members of the eicosanoid family of bioactive signaling molecules derived from the substrate arachdonic acid (AA). LTs are lipid signaling molecules that contribute to the initiation and amplification of the innate and adaptive immune responses. LTs are mediators of asthma and allergic rhinitis, as demonstrated by clinical studies, and studies using knockout animals for the biosynthetic enzymes and receptors. Recently, they have been implicated in the chronic vascular inflammation of atherosclerosis. LTs B4, C4, D4 and E4 function to recruit and activate leukocytes in inflamed tissue, and also regulate the function of endothelial cells, and vascular and airway smooth muscle. The formation of LTC4, the parent cysteinyl LT, requires the functional interaction of at least four proteins on the nuclear envelope. These are cytosolic phospholipase A2 (cPLA2), 5-lipoxygenase (5-LO), the 5- lipoxygenase-activating protein (FLAP), and LTC4 synthase; the metabolism of LTA4 by LTA4 hydrolase (LTA4-H) yields LTB4. Recently, we have shown that 5-LO, FLAP, and LTC4 synthase are assembled in novel macromolecular complexes on the nuclear envelope to initiate LT synthesis. These complexes include an additional FLAP-associated protein, Associated Protein-10 kDa (AP-10), and other proteins. AP-10 dissociates from FLAP concurrent with complex formation, suggesting it has an important regulatory role in LT formation. However, neither its identity nor the signals controlling its dissociation from FLAP are known. The intracellular signals that initiate and sustain the association of 5-LO with FLAP and also the overall assembly of the complex are unknown. One possibility is that sustained intracellular calcium levels are required for both membrane targeting of 5-LO and its association with FLAP. Alternatively, the movement of 5-LO to the nuclear envelope and its incorporation into LT membrane synthetic may be under separate controls. The broad, long-term objective of this proposal is to determine how the assembly of LT membrane synthetic complexes is regulated and to identify each of the components and their roles.